GB2408420A

GB2408420A - Determining a power relationship linking the transmit powers of user data and associated control data

Info

Publication number: GB2408420A
Application number: GB0327155A
Authority: GB
Inventors: Walter Featherstone; Simon Burley; Jonathan Wallington
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2003-11-21
Filing date: 2003-11-21
Publication date: 2005-05-25
Anticipated expiration: 2023-11-21
Also published as: GB2408420B; GB0327155D0

Abstract

In a communication system where user data and associated control data are transmitted from one entity to another, a power relationship linking the transmit powers of the user data and associated control data is determined at least partly dependent on a received quality of the associated control data. For example, if the bit error rate (BER) of the received control data is found to be below a desired threshold, an increase in the control transmit power is required and a new power relationship (e.g. a different offset or ratio) is determined which enables the required increase in the control transmit power whilst maintaining the data transmit power at a level set by an outer power control loop. Conventionally, a set relationship is established between the data and control transmit powers and the transmit power of the data channel is optimised using inner and outer loop power control. However, in such systems the control power is not optimised as it merely follows the data power according to the set relationship. Implementation of the described method results in the ability to maintain the transmit power of the user data, (e.g. on a Dedicated Physical Data Channel (DPDCH) in UMTS), at an optimum power level set by a power control process, whilst ensuring that associated control data, (e.g. on a Dedicated Physical Control Channel (DPCH)), is also transmitted at an optimum power level. The invention ensures reception of the user data and control data with an acceptable error rate causing minimum interference to other users. New quality targets may also be generated for the power loop control processes.

Description

METHOD OF POWER CONTROL AND CORRESPONDING POWER

CONTROLLER

The present invention relates to a method of power control in a communication system and to a corresponding power controller.

Many cellular communication systems are now available or are planned for the future. In a cellular communication system, such as the exemplary cellular communication system shown in Figure 1, the whole coverage area 2 of the communication system is divided into plurality of cells 4, 6, 8, 10, each cell 4, 6, 8, 10 having a respective serving base transceiver station 12, 14, 16, 18 to support communication with user terminals 20 within the cell. The term uplink 22 defines communications in the direction from a user terminal to the base station: the term downlink 24 defines communications in the direction from the base station to the user terminal.

Typically, the user terminals 20 are mobile user terminals that are able to move within the whole coverage area 2 of the cellular communication system. Since a user terminal may be located anywhere within the cell served by a base transceiver station, the radio propagation loss between the user terminal and the base transceiver station may vary significantly. Furthermore, fluctuations due to multi-path fading result in short term variations in radio propagation loss. In order to control interference within the communication system and overcome the near- far problem, generally it is desirable to implement power control in a radio communication system such that the power used to transmit from the user terminal on the uplink and from the base transceiver station on the downlink adjusted to a level that is just sufficient to allow recovery of information from the received signals at an acceptable error rate. This enables reliable operation of the communication system while minimizing interference caused to other users by excessive signal levels.

In some communication systems, user data (which may include speech data) and associated control information are sent on respective data and control channels in both the uplink and the downlink directions. Generally, there is an established relationship, such as an offset or ratio, between the powers at which the data and control channels are transmitted and power control is implemented to ensure accurate reception of the data channel.

This technique enables the transmit powers for both the data channel and the control channel to be established easily while implementing power control in the communication system to ensure adequate reception of user data. However, since the power control is designed to ensure adequate reception of the data channel only, and the control channel transmit power is merely related to the data channel transmit power by the established relationship, the control channel transmit power may be greater than or less than the transmit power required to ensure accurate reception of the control channel data. This may result in unnecessary interference in the communication system owing to a higher than necessary transmit power, or inaccurate reception of control channel data owing to a lower than necessary transmit power.

The present invention seeks to alleviate at least some of the disadvantages of

the prior art.

According to a first aspect of the invention there is provided a method of power control in a communication system comprising the steps of: determining a power relationship linking the power at which user data and associated control data are transmitted at least partly dependent on a received quality of associated control data; and informing a transmitting entity of the determined power relationship.

According to a second aspect of the invention there is provided a power controller in a communication system comprising: value determiner for determining a power relationship linking the power at which user data and associated control data are transmitted at least partly dependent on a received quality of associated control data; and for informing a transmitting entity of the determined power relationship.

For a better understanding of the present invention, and to show how it may be brought into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows an exemplary cellular communication system; Figure 2 shows an exemplary elements of a cellular communication system adapted to implement an embodiment; Figure 3 shows a method in accordance with an embodiment; Figure 4 shows exemplary initial uplink power levels; Figure 5 shows exemplary uplink power levels after application of the method as shown in Figure 3; Figure 6 shows exemplary initial downlink power levels; Figure 7 shows exemplary downlink power levels after application of the method as shown in Figure 3.

One cellular communications system in which user data (which may include speech data) and associated control information are sent on respective data and control channels in both the uplink and the downlink directions is the Universal Mobile Communication System (UMTS) that is currently undergoing standardization under the Third Generation Partnership Project (3GPP) of the European Telecommunication Standards Institute (ETSI).

Although the embodiments will be described below within the context of a UMTS system employing COMA radio access technology, it should be noted that the invention is not intended to be limited thereto, and may be applicable to other systems such as other COMA systems and also to Orthogonal Frequency Division Multiplex (OFDM) and Time Division Multiple Access (TDMA) systems.

In fact, the method described herein may be applied to any communication system in which control data and user data (or a control channel and a data channel) are multiplexed, for example by quadrature phase, time, frequency, code and so on, as will be apparent to a skilled person.

UMTS is based on code division multiple access (CDMA) radio access technology. In CDMA communication systems, uplink and downlink control or data channels typically use a large bandwidth of radio frequency spectrum, for example in the region of 5MHz for UMTS channels.

In CDMA communication systems, signaling and/or user data is multiplied by a respective code prior to being transmitted on uplink or downlink control or data channels. The effect of the multiplication is to spread the original data over a wide bandwidth. At the receiver, the received wideband signal is multiplied by the same code that was used in the transmitter, resulting in the recovery of the original signaling or traffic data.

Separation between different channels is achieved by allocating a different code to each channel. Such channels are called code channels. Since different codes are used for different code channels, different code channels may be kept distinct from each other even though they are transmitted using the same radio frequency spectrum.

A Dedicated Physical Channel (DPCH) may be set up between a base station and a user terminal to transfer user data (which may include speech data). The DPCH comprises a Dedicated Physical Data Channel (DPDCH) for transfer of the user data and a Dedicated Physical Control Channel (DPCCH) for transfer of associated control and signaling information. The uplink DPDCH and DPCCH are transmitted on separate code channels, whereas the downlink DPDCH and DPCCH are transmitted on a single code channel in a time-multiplexed manner. s

Figure 2 shows exemplary elements of a UMTS system adapted to implement an embodiment.

A user terminal 20 (called a UE in UMTS terminology) is within a cell 4 supported by a base transceiver station 12 (called a node B in UMTS terminology). The node B is operably coupled to a base station controller 26 (called a RNC in UMTS terminology), which is in turn operably coupled to the core network 28 of the communication system. The RNC 26 controls the operation of the node B 12.

The node B 12 is provided with a control quality measurement module 30 that measures the quality of the signal received on the uplink DPCCH in the illustrative embodiment. The control quality measurement module 30 may be an existing module of the node B 12, such as provided for implementing the inner power control loop in a UMTS system, or may be a new module. The control quality measurement module 30 may be implemented as a software module running on a dedicated processor, or as a software module forming part of a larger software program running on a node B processor.

The control quality measurement module 30 may measure the Bit Error Rate (BER) of all or part of the received control channel signal for example. In one embodiment, bit error rate of the control channel pilot bits is measured. Thus, for example, the size of the pilot correlator peak may be determined and used as a measure of control channel quality.

In addition, the node B is provided with an inner power control loop controller 32 (!PCL controller 32). As will be known to a skilled person, the IPCL controller 32 controls the inner power control loop for uplink signals. The IPCL controller 32 is provided with a quality target, typically a signal to interference ratio (SIR) target, for the DPCCH by an outer power control loop controller (not shown) in the RNC 26. In operation, the IPCL controller 32 compares measurements of SIR on the received DPCCH with the SIR target set by the outer power control loop controller. The IPCL controller 32 signals to the UE 20 to increase the UE transmit power if the measured SIR is less than the SIR target, and signals the UE 20 to decrease the UE transmit power if the measured SIR is less than the SIR target.

The RNC 26 is provided with a value determiner 34. The value determiner 34 may be implemented as a processor running software implementing the method of an embodiment described below with reference to Figure 3, to determine power relationship information and, optionally, quality target information. The processor may be a dedicated processor, or the software implementing the method of the embodiment may be a software module forming part of a larger software program running on an RNC processor. In particular, the value determiner 34 may form part of the outer power control loop controller (not shown explicitly).

In addition, it should be noted that although in the illustrated embodiment the value determiner 34 is shown functionally as part of the RNC (or base station controller) 26, in fact it would be possible in alternative embodiments to implement the functionality of the value determiner 34 in the node B (or base transceiver station) 12, or in another suitable network element.

The value determiner 34 is operably coupled to the control quality measurement module 30 to receive measurements of control channel quality. In addition, the value determiner 34 may be operably coupled to the IPCL controller 32 to provide quality target information thereto, in some embodiments of the invention.

The value determiner 34 is also operable to provide the UE 20 with the determined power relationship information.

The UE 20 is provided with a downlink control quality measurement module 36, an inner power control loop (IPCL) controller 38 and, optionally, a value determiner 40 in one embodiment.

The downlink control quality measurement module 36 measures the quality of the signal received on the downlink DPCCH in the illustrative embodiment. The control quality measurement module 36 may be an existing module of the UE 20, such as provided for implementing the inner power control loop measurements in a UMTS system, or may be a new module. The control quality measurement module 36 may be implemented as a software module running on a dedicated processor, or as a software module forming part of a larger software program running on a UE processor.

The control quality measurement module 36 may measure the Bit Error Rate (BER) of all or part of the received control channel signal for example. In one embodiment, bit error rate of the control channel pilot bits is measured. Thus, for example, the size of the pilot correlator peak may be determined and used as a measure of control channel quality.

In addition, the UE 20 is provided with an inner power control loop controller 38 (IPCL controller 38).As will be known to a skilled person, the IPCL controller 38 controls the inner power control loop for downlink signals. The IPCL controller 38 is provided with a quality target, typically a signal to interference ratio (SIR) target, for the downlink DPCCH by an outer power control loop controller (not shown) in the UE 20. In operation, the IPCL controller 38 compares measurements of SIR on the received DPCCH with the SIR target set by the outer power control loop controller. The IPCL controller 38 signals to the node B 12 to increase the node B transmit power if the measured SIRis less than the SIR target, and signals the node B 12 to decrease the node B transmit power if the measured SIRis less than the SIR target.

The UE 20 may also be provided with a value determiner 40. The value determiner 40 may be implemented as a processor running software implementing the method of an embodiment described below with reference to Figure 3, to determine power relationship information and optionally quality target information. The processor may be a dedicated processor, or the software implementing the method of the embodiment may be a software module forming part of a larger software program running on a UE processor. In particular, the value determiner 40 may form part of the UE outer power control loop controller (not shown explicitly).

As will become apparent from the discussion below, in some embodiments the UE is provided with a value determiner 40 which implements the method as described below with reference to Figure 3 in respect of the downlink. However, in other embodiments, the method as described below with reference to Figure 3 in respect of the downlink may be implemented by value determiner 34 in the RNC 26, or another suitable module in the RNC 26 or any other network element.

The value determiner 40, if provided, is operably coupled to the control quality measurement module 36 to receive measurements of control channel quality. In addition, the value determiner 40 may be operably coupled to the IPCL controller 38 to provide quality target information thereto, in some embodiments of the invention. The value determiner 40 is also operable to provide the node B 12 with the determined power relationship information.

A method carried out by the value determiner 34 in respect of the uplink in accordance with an embodiment is shown in Figure 3.

Firstly, in step s2, the value determiner 34 receives measured control quality information from control quality measurement module 30. As described above, such control quality information may relate to the received BER on the DPCCH or may relate to the magnitude of the output of a pilot bit correlator for the DPCCH, or any other quality measurement.

In step s4 the value determiner 34 determines new power relationship values to be used by the UE 20 when transmitting the unlink channels. Typically, in the illustrative embodiment described with reference to the UMTS communication system, the new power relationship values are new values of pd and pc that determine the relative ratio or scaling of the transmit powers of the DPDCH and the DPCCH respectively. However, other power relationship values, such as offset values may be used in other embodiments.

The value determiner 34 may determine the new power relationship values by comparing the received measured control quality information with one or more thresholds. The threshold or thresholds typically will relate to a quality measurement that corresponds to an acceptable error rate on the control channel, but which is not so high that it causes excessive interference to the rest of the communication system.

Thus if the received measured control quality is better than a threshold, the control channel power level may be reduced. In order to maintain the data channel power levels corresponding to the power levels set by the normal outer power control loop processes, the power relationship values must be altered.

Thus, in this example, the value of,Bc must be reduced relative to pd Alternatively, if the received measured control quality is worse than a threshold, which may be the same or a different threshold, the control channel power level may be increased. In order to maintain the data channel power levels corresponding to the power levels set by the normal outer power control loop processes, the power relationship values must be altered. Thus, in this example, the value of pc must be increased relative to pd.

Step 6 may be omitted in some embodiments of the invention. In step s6 the value determiner 34 may determine a new control quality target ie a new SIR target, for the IPCL controller 32. This new quality target corresponds to the new expected signal level after the alteration in control channel transmit power has been implemented as a result of the alteration in the power relationship values as described above.

The value determiner 34 may determine the new control quality target by comparing the received measured control quality information with one or more thresholds. The threshold or thresholds typically will relate to a quality measurement that corresponds to an acceptable error rate on the control channel, but which is not so high that it causes excessive interference to the rest of the communication system.

Thus if the received measured control quality is better than a threshold, the control quality target will be reduced to correspond with the reduction in expected control channel power implemented as a result of the alteration in the power relationship values as described above. Alternatively, if the received measured control quality is worse than a threshold, which may be the same or a different threshold, the control quality target will be increased to correspond with the reduction in expected control channel power implemented as a result of the alteration in the power relationship values as described above.

In will be apparent that, in embodiments that include step so, steps s4 and s6 may be carried out in any order, and indeed at least parts of s4 and s6 may be combined. So, for example, the comparison of the received measured control quality may be carried out only once, and the results used to determine both the new quality target level and the offset values required to maintain the data channel power levels as set by the normal outer power control loop processes. In particular in one embodiment, a new level for the DPCCH power may be set as a first step, and in a second step new power relationship values and quality control targets may be set dependent on the new DPCCH power level.

In step s8 information relating to the power relationship values is passed to the transmitting party, i.e. the UE 20 in the case of the unlink, by the value determiner 34. In the exemplary described embodiment of the UMTS system this information may be passed to the UE 20 as updated, 0 and,Bc values in a channel configuration message sent by the value determiner 34. However uplink power relationship value information may be transferred to the UE 20 in any other suitable way in other communication systems.

In embodiments in which new quality control targets are determined in step so, the new control quality target information is passed to the IPCL controller 32 by the value determiner 34, for use by the IPCL controller 32 in the inner power control loop process. This control quality target information may be passed to the IPCL controller 32 in the form of a new SIR target or in the form of an instruction to increment or decrement the SIR target used in the IPCL process.

In addition, it may be necessary in some embodiments to also inform the outer power control loop controller in the RNC (not shown) of the alteration in the SIR target.

Thus in accordance with the method described above, the uplink control channel transmit power may be optimized so as to ensure that the control channel information can be recovered with an acceptable error rate, while minimizing interference caused by control channel transmissions. At the same time, the data channel power is maintained at the levels set by the outer power control loop, thus ensuring that the outer power control loop operation is maintained to achieve acceptable reception of user data on the DPDCH.

Figures 4 and 5 illustrate the effect on the uplink DPCH power levels as a result of the operation of the invention.

Figure 4 shows the initial power relationship between the DPDCH and the DPCCH in the exemplary embodiment described with respect to the UMTS system. As mentioned previously, in the exemplary UMTS system, the power relationship between the DPDCH and the DPCCH on the uplink is governed by the relative values of pd and pc. Thus, the powers of the DPDCH and the DPCCH are respectively scaled by the values of pd and pc by the UE 20 and the DPCCH power is adjusted to follow the inner loop power commands received from the IPCL controller 32. In this way, the DPDCH power is maintained at an optimum level by means of the measurement of received error rate on the DPDCH used by the outer power control loop.

When the DPCH power levels as shown in Figure 4 are received at the node B 12, the normal power control loop processes are executed. Thus, the SIR of the DPCCHis measured, compared with the SIR target by the IPCL controller 32 and power up or power down signals are sent to the UE 20 to maintain the received SIR at or around the SIR target. In addition, the error rate (for example the block error rate) on the DPDCHis measured periodically and compared with a DPDCH error rate target (that equates to sufficiently good reception of the user data) by the outer power control loop (OPCL) controller (not shown) in the RNC 26. The SIR target is adjusted by the OPCL controller so as to maintain the received DPDCH error rate at or around the DPDCH error rate target, and the new SIR target (or increment SIR targeVdecrement SIR target commands, as appropriate) are sent by the OPCL controller to the IPCL controller 32. In this way, the DPDCH power levels are maintained at levels that are sufficient to ensure adequate reception of the user data, but that cause the minimum interference to other users.

In addition, the method of the present invention described above in connection with Figure 3 is implemented. Thus, the control quality measurement module 30 measures the received quality of the DPCCH, for example the error rate (for example the bit error rate) on the DPCCH or by measuring the height of the output of a pilot correlator for the DPCCH and this measurement is forwarded to the value determiner 34. The value determiner 34 can then determine whether new power relationship values and, optionally, new target values are required i.e. whether or not the DPCCH power level is set at a level that is sufficient to ensure adequate reception of the control channel data, but that causes the minimum interference to other users.

If, for example, the value determiner 34 establishes that the DPCCH power level is insufficient to ensure adequate reception of the control channel data, the DPCCH power level should be raised. In order to achieve this, new power relationship values are established to enable the transmit power of the DPCCH to be increased whilst maintaining the transmit power of the DPDCH to be maintained at the level determined by the outer power control loop. Thus in the exemplary case, pc will be increased with respect to pd.

The new power levels resulting from the implementation of the new values by the IPCL controller 32 and the UE 20 are illustrated in Figure 5. Thus, the DPCCH power level in Figure 5 has been raised with respect to the DPCCH power level in Figure 4: however, the DPDCH power level in Figure 5 has been maintained at the same level as the DPDCH power level in Figure 4.

Since the transmit power of the DPCCHis raised, in the exemplary illustration, the SIR target used by the IPCL controller 32 must be raised correspondingly.

One way of achieving this rise in the SIR target used by the IPCL controller 32 is for the new SIR target, or the required change in the SIR target, to be determined in optional step s6, and communicated to the IPCL controller 32 in optional step s10, of the method shown in Figure 3.

However, it is not necessary in all embodiments to explicitly change the SIR target, since the required alteration of the SIR target will occur in view of the operation of the outer power control loop. Thus, if optional steps s6 and s10 are omitted from the method set out in Figure 3, the power relationship only will be altered and communicated to the UE 20 in steps s4 and s8. The UE20 will scale the DPDCH and DPCCH using the new power relationship values, but will still transmit the DPCCH at the same power as before, in accordance with the normal power control process. The change in the power relationship values in the exemplary embodiment of an increase of,Bc with respect to p will therefore lead to a temporary effective decrease in the transmitted DPDCH power. This is liable to cause a temporary decrease in the received quality of the DPDCH ie the Block Error Rate will increase and the OPCL controller in the RNC will then raise the SIR target set for the IPCL controller 32 to a new, appropriate, level in accordance with the normal operation of the outer power control loop.

Clearly, although the description above relates to a situation in which the DPCCH power is to be raised, the method described above may also used in implementing a decrease in the DPCCH power to avoid excessive interference being caused to other users.

A method carried out in respect of the downlink in accordance with an embodiment will now be described with reference to Figure 3.

In some embodiments the method may be carried out by value determiner 34 in the RNC 26, and in other embodiments the method may be carried out by value determiner 40 in the UE 20.

Firstly, in step s2, the value determiner 34 or value determiner 40 receives measured downlink control quality information from downlink control quality measurement module 36. As described above, such control quality information may relate to the received BER on the DPCCH or may relate to the magnitude of the output of a pilot bit correlator for the DPCCH, or any other quality measurement. Clearly, value determiner 40 may receive the measured downlink control quality information directly from the downlink control quality measurement module 36, and the value determiner 34 may receive the measured downlink control quality information from the downlink control quality measurement module 36 via existing signaling, if available, or proprietary signaling between the UE 20 and the RNC 26.

In step s4 the value determiner 34 or value determiner 40 determines new power relationship values to be used by the node B 12 when transmitting the downlink channels. Typically, in the illustrative embodiment described with reference to the UMTS communication system, the new power relationship values are new power offset values of P01, P02 etc that determine the offset between the transmit powers of the DPDCH and the DPCCH respectively. However, other power relationship values may be used in other embodiments or other communication systems.

The value determiner 34 or value determiner 40 may determine the new power relationship values by comparing the received downlink measured control quality information with one or more thresholds. The threshold or thresholds typically will relate to a quality measurement that corresponds to an acceptable error rate on the control channel, but which is not so high that it causes excessive interference to the rest of the communication system.

Thus if the received measured control quality is better than a threshold, the control channel power level may be reduced. In order to maintain the data channel power levels corresponding to the power levels set by thenormal outer power control loop processes, the power relationship values must be altered.

Thus, in this example, the value of the offsets may be decreased (for positive offset values) or increased (for negative offset values). Alternatively, if the received measured control quality is worse than a threshold, which may be the same or a different threshold, the control channel power level may be increased.

The inclusion of step 6 may be omitted in some embodiments of the invention. In step s6 the value determiner 34 or value determiner 40 may determine a new control quality target ie a new SIR target, for the IPCL controller 40. This new quality target corresponds to the new expected signal level after the alteration in control channel transmit power has been implemented as a result of the alteration in the power relationship values as described above.

The value determiner 34 or value determiner 40 may determine the new control quality target by comparing the received measured control quality information with one or more thresholds. The threshold or thresholds typically will relate to a quality measurement that corresponds to an acceptable error rate on the control channel, but which is not so high that it causes excessive interference to the rest of the communication system.

In will be apparent that, in embodiments that include step so, steps s4 and s6 may be carried out in any order, and indeed at least parts of s4 and so may be combined. So, for example, the comparison of the received measured control quality may be carried out only once, and the results used to determine both the new quality target level and the offset values required to maintain the data channel power levels as set by the normal outer power control loop processes. In particular in one embodiment, a new level for the DPCCH power may be set as a first step, and in a second step new power relationship values and quality control targets may be set dependent on the new DPCCH power level.

In step s8 information relating to the power relationship values is passed to the transmitting party, i.e. the node B 12 in the case of the downlink, by the value determiner 34 or the value determiner 40. Clearly, either value determiner 34 or value determiner 40 may pass the power relationship values to the node B via existing signaling, if available, or otherwise using proprietary signaling.

In the exemplary described embodiment of the UNITS system this information may be passed to the node B as updated power offset values P01, P02 etc. However downlink power relationship value information may be transferred to the node B 12 in any other suitable way in other communication systems.

In embodiments in which new quality control targets are determined in step so, the new control quality target information is passed to the IPCL controller 38 for use by the IPCL controller 38 in the downlink inner power control loop process.

This control quality target information may be passed to the IPCL controller 38 in the form of a new SIR target or in the form of an instruction to increment or decrement the SIR target used in the IPCL process. Clearly, value determiner 40 may pass the new quality control target information directly to the IPCL controller 38, and the value determiner 34 may pass the new quality control target information to the IPCL controller 38 via existing signaling, if available, or proprietary signaling between the UE 20 and the RNC 26.

In addition, it may be necessary in some embodiments to also inform the outer power control loop controller in the UE 20 (not shown) of the alteration in the SIR target.

Thus in accordance with the method described above, the downlink control channel transmit power may be optimized so as to ensure that the control channel information can be recovered with an acceptable error rate, while minimizing interference caused by control channel transmissions. At the same time, the data channel power is maintained at the levels set by the outer power control loop, thus ensuring that the outer power control loop operation is maintained to achieve acceptable reception of user data on the DPDCH.

Figures 6 and 7 illustrate the effect on the downlink DPCH power levels as a result of the operation of the invention.

Figure 6 shows the initial power relationship between the downlink DPDCH and the DPCCH in the exemplary embodiment described with respect to the UMTS system. As mentioned previously, in the exemplary UMTS system, the power relationship between the DPDCH and the DPCCH on the uplink is governed by the power offsets P01, P02 etc. In the exemplary illustrated embodiment, power offset P01 relates to the power offset between the DPDCH and the Transport Format Indicator (TFCI) bits of the DPCCH; power offset P02 relates to the power offset between the DPDCH and the power control (TPC) bits of the DPCCH; power offset P03 relates to the power offset between the DPDCH and the pilot bits of the DPCCH.

When the DPCH power levels as shown in Figure 6 are received at the UE 20, the normal power control loop processes are executed. Thus, the SIR of the downlink DPCCHis measured, compared with the SIR target by the IPCL controller 38 and power up or power down signals are sent to the node B to maintain the received SIR at or around the SIR target. In addition, the error rate (for example the block error rate) on the DPDCHis measured periodically and compared with a DPDCH error rate target (that equates to sufficiently good reception of the user data) by the outer power control loop (OPCL) controller (not shown) in the UE 20. The SIR target is adjusted by the OPCL controller so as to maintain the received DPDCH error rate at or around the DPDCH error rate target, and the new SIR target (or increment SIR targeVdecrement SIR target commands, as appropriate) are sent by the OPCL controller to the IPCL controller 38. In this way, the DPDCH power levels are maintained at levels that are sufficient to ensure adequate reception of the user data, but that cause the minimum interference to other users.

In addition, the method of the present invention described above in connection with Figure 3 is implemented. Thus, the control quality measurement module 36 measures the received quality of the DPCCH, for example the error rate (for example the bit error rate) on the DPCCH or by measuring the received power for example by measuring the height of the output of a pilot correlator is also measured and this measurement is forwarded to the value determiner 34 or value determiner 40, as discussed above. The value determiner 34 or value determiner 40 can then determine whether new power relationship values and, optionally, new target values are required i.e. whether or not the DPCCH power level is set at a level that is sufficient to ensure adequate reception of the control channel data, but that causes the minimum interference to other users.

If, for example, the value determiner 34 or value determiner 40 establishes that the DPCCH power level is insufficient to ensure adequate reception of the control channel data, the DPCCH power level should be raised. In order to achieve this, new power relationship values are established to enable the transmit power of the DPCCH to be increased whilst maintaining the transmit power of the DPDCH to be maintained at the level determined by the outer power control loop. Thus in the exemplary case, at least one of the power offset values P01, P02 etc will be increased.

The new power levels resulting from the implementation of the new values by the IPCL controller 38 (if necessary) and the node B 12 are illustrated in Figure 7.

Thus, the DPCCH power level in Figure 7 has been raised with respect to the DPCCH power level in Figure 6: however, the DPDCH power level in Figure 7 has been maintained at the same level as the DPDCH power level in Figure 6.

Since the transmit power of the DPCCH is raised, in the exemplary illustration, the SIR target used by the IPCL controller 38 must be raised correspondingly.

One way of achieving this rise in the SIR target used by the IPCL controller 38 is for the new SIR target, or the required change in the SIR target, to be determined in optional step s6, and communicated to the IPCL controller 38 in optional step s10, of the method shown in Figure 3.

However, it is not necessary in all embodiments to explicitly change the SIR target, since the required alteration of the SIR target will occur in view of the operation of the outer power control loop. Thus, if optional steps so and s10 are omitted from the method set out in Figure 3, the power relationship only will be altered and communicated to the node B 12 in steps s4 and s8. The node B 12 will use the new offset values, but will still transmit the DPCCH at the same power as before, in accordance with the normal power control process. The change in the power relationship values in the exemplary embodiment of an increase of the offsets P01, P02 etc will therefore lead to a temporary effective decrease in the transmitted DPDCH power. This is liable to cause a temporary decrease in the received quality of the DPDCH ie the Block Error Rate will increase and the OPCL controller in the UE 20 will then raise the SIR target set for the IPCL controller 38 in accordance with the normal operation of the outer power control loop.

Thus the implementation of the described method results in the ability to maintain the transmit power of a user data, for example on a data channel such as the DPDCH in UMTS, at a level set by power control processes at an optimum power level to ensure reception of the user data with an acceptable error rate causing minimum interference to other users, whilst ensuring that associated control data is also transmitted at an optimum power level to ensure reception of the control data with an acceptable error rate causing minimum interference to other users.

Although the exemplary embodiments have been described with respect to implementation within a UMTS communication system, it will be apparent that the UMTS system is used merely as an exemplary communication system and the invention may be applied to other communication systems.

In addition, although in the exemplary illustrative UMTS system, the uplink uses a power ratio to determine the power relationship between the traffic data and the control data, and the downlink uses power offsets to determine the power relationship between the traffic data and the control data, in fact the invention may be applied to any type of power relationship, including but not limited to offsets and ratios. In addition, the power relationships may be the same or may be different in the uplink and downlink. In addition, in some communication systems the invention may be applied in only one direction i.e. to the uplink only, or to the downlink only within the discretion of the skilled person.

Claims

CLAIM

1. A method of power control in a communication system comprising the steps of: determining a power relationship linking the power at which user data and associated control data are transmitted at least partly dependent on a received quality of associated control data; and informing a transmitting entity of the determined power relationship.

2. The method as claimed in claim 1, where the power relationship is an offset between the user data transmit power and the control data transmit power.

3. The method as claimed in claim 2, where offset is defined by a ratio between the user data transmit power and the control data transmit power.

4. The method as claimed in claim 3, where the ratio is defined by scaling factors applied to the user data transmit power and the control data transmit power.

5. The method as claimed in claim 4, where the scaling factors applied to the user data transmit power and the control data transmit power are p and pc respectively.

6. The method as claimed in any preceding claim, where a control channel bit error rate (BER) is used to evaluate the received quality of the control data.

7. The method as claimed in any preceding claim, also comprising the step of altering a power control loop quality target for the received control data dependent on the received quality of the control data.

8. The method as claimed in any preceding claim, also comprising the step of altering a power control loop quality target for the received control data dependent on the determined power relationship.

9. The method as claimed in claim 7 or 8, where the power control loop quality target is an inner power control loop quality target.

10.The method as claimed in claim 7, 8 or 9, where the power control loop quality target is a signal to interference (SIR) quality target.

11.A storage medium storing processor-implementable instructions for controlling a processor to carry out the method of any preceding claim.

12.A power controller in a communication system comprising: value determiner for determining a power relationship linking the power at which user data and associated control data are transmitted at least partly dependent on a received quality of associated control data; and for informing a transmitting entity of the determined power relationship.

13.The power controller as claimed in claim 12, wherein the value determiner also alters a power control loop quality target for the received control data dependent on the received quality of the control data.